The ground wire in a boiler system is typically blue. This color-coding standard is in accordance with the National Electrical Code (NEC), which specifies that blue is the designated color for grounding wires in the United States. The NEC is a set of regulations for electrical installations, and it is widely adopted by states and local jurisdictions. The use of standardized colors for electrical wiring helps to ensure safety and ease of troubleshooting.

The reason for using blue as the ground wire color is to clearly differentiate it from other wires in the system. Ground wires are used to provide a safe path for electrical current to flow in the event of a fault, thereby preventing electrical shocks and fires. By using a distinct color, it becomes easier for electricians and maintenance personnel to identify and connect the ground wire correctly.

According to the NEC, the color code for grounding wires is as follows:

Solid blue: Ground wire

Solid green: Equipment grounding conductor

Green with yellow stripe: Grounding electrode conductor

These color codes are designed to be universally recognized, reducing the likelihood of errors during installation and maintenance. The use of standardized color codes is not only a safety measure but also a practical one, as it simplifies the process of identifying and working with electrical systems.

In addition to the NEC, other organizations and standards may also adopt these color codes. For example, the American National Standards Institute (ANSI) has recognized the NEC's color codes for grounding wires. This further reinforces the importance of using blue for ground wires in boiler systems and other electrical installations across the United States.